Gates of the type concerned in the present context are in particular overhead gates, although they may also be vertical roll-up gates, sliding gates, etc., have a motorized mechanism that drives a panel or similar structure back and forth along a particular path between two limiting positions, and operate with limit switches that stop, by means of a radio signal for example, the motor that is responsible for the motion of the panel as soon as the panel arrives in its prescribed limiting position.
The limit switches are mounted in the vicinity of the limiting positions actually assumed by the gate panel, with a switched component on the frame or track of the gate and a switching component on the panel. Switched components accordingly mounted near the bottom of the opening to be closed off by the gate and at the edge of the gateway are, however, subject to damage, especially in heavy-industrial applications. Since they are also more exposed to contamination and splashing, both mechanical limit switches and those activated for example by light barriers entail associated problems.
It is of particular significance that positioning the limit switches in the vicinity of the frame or track and activating them by means of the panel itself not only entails additional installation labor after the gate has been mounted but also and in particular demands alignment and adjustment that require a lot of time and effort on site and are not within the capabilities of the average installer, who is more accustomed to less skilled labor. The small volume of space ordinarily available also makes for problems.
Simulating the motion of the gate panel, exploiting, that is, a parameter that corresponds to that motion and is derived from its drive mechanism although greatly reduced in scale to rotate or displace a certain component to an extent that represents the actual measured path traveled by the panel, has been proposed. A simulating component of this type thus also travels between two limiting positions that correspond to those of the panel, at which points they activate switchgear that accordingly reproduce the limiting positions of the panel.
Although a simulator, which is preferably positioned in the vicinity of the drive mechanism or its controls, is protected from contamination, dirt, and moisture, it demands especially precise adjustment in relation to the panel once the gate has been installed to the extent for instance that the point at which the panel begins to move corresponds precisely with the point at which the displacement of the simulator commences. At the path-reduction ratios involved, even slight discrepancies will allow the panel to travel beyond its limiting position and collide against the end of its track or against other objects. What is called a zero match between the panel and the moving simulator component accordingly demands special care and sensitivity that is difficult to obtain in such a coarse operation as mounting a gate.